The present invention relates to an anti-theft system for cars, and more particularly, to a cipher type anti-theft system that uses in-car wiring to transmit a cipher for arming and disarming the car. Any general consumer can easily install the anti-theft system in a car without the help of a skilled worker or the need to build any additional wiring. No additional wiring would exist in the car to form any trace for a theft.
To prevent a car from being stolen, a common practice is to install an anti-theft system in the car. Generally, when a car is touched, a moved or intruded without authorization, the anti-theft system installed in the car would emit sound or give an alarm and cut off one of more major circuits needed to start the card, so as to stop the thief from driving the car away. There are also deluxe cars installed with anti-theft system that requires input of a correct cipher to disarm the car from the anti-theft system. FIG. 1 shows a basic design for such cipher type anti-theft systems currently available in the market. As shown, the conventional cipher-type anti-theft system includes a control module that is connected to at least one cut-off relay via wires, and the at least one cut-off relay is connected to the starter, fuel pump or igniter of the car. A cipher is input via an external interface, such as a keypad, an input socket or a radio receiver and sent to the control module via a wire. The control module controls the at least one cut-off relay through wires, so that at least one cut-off relay is cut off to disable the starter, igniter or fuel pump of the car and therefore protects the car from being driven away by a thief.
The following are some of the disadvantages of the above-described conventional cipher type anti-theft systems:
1. All the currently available cipher type anti-theft systems have a control module that requires additional wiring for installing it on a car. The installation is complicated and time-consuming and must be done by a skilled worker. The conventional cipher type anti-theft systems therefore require high installation cost.
2. In consideration of the power supply to the control module and the control of different parts by the control module, it is a common practice to locate the control module below the instrument panel or a front seat close to the external keypad or input socket for inputting a cipher. A thief entering the car may easily find the external keypad or input socket and then trace the wire or status LED to the control module to locate and destroy it. When this happens, the cut-off relay would automatically close the circuit within a short time and therefore lose its anti-theft function.
3. To enhance the function of the cipher type anti-theft system, there is developed a special externally cut-off relay. However, to simplify and shorten wiring between the control module and the external relay, the external relay is usually installed at a position close to the control module or the ignition switch of the car. The relay mounted at such positions can be very easily located and removed or disabled by causing it to short-circuit. For an experienced theft, the conventional cipher type anti-theft system is almost useless.
In brief, all the currently available cipher type anti-theft systems that require additional wiring just could not guard the car against the theft at all. There are cars installed with such conventional cipher type anti-theft system being intruded and driven away within a very short time, because the theft can easily intrude the car and quickly open the hood to cut off the alarm siren before return to the car to quickly locate and destroy the control module and all the cut-off relays of the anti-theft system by tracing any additional wiring in the car.
It is therefore tried by the inventor to develop an improved cipher type anti-theft system for cars that eliminates the drawbacks existing in the convention cipher type anti-theft systems.
A primary object of the present invention is to provide a cipher type anti-theft system for cars that can be easily installed in the car by any general consumer without the need of any additional wiring. A specific cipher can be transmitted through in-car wiring and there is no way for a theft to find out the anti-theft system by tracing the additional anti-theft wires in the car.
Another object of the present invention is to provide a cipher type anti-theft system for cars, an embodiment of which uses a cigarette lighter holder in the car as an interface to input and transmit a specific cipher.
To achieve the above and other objects, the present invention mainly includes an encoder/transmitter and at least one decoder cut-off relay. The encoder/transmitter may generate a cipher and convert the same from digits to analog signals for loading onto in-car wiring. The at least one decoder cut-off relay may be installed at any point on any power supply circuit needed to start the car in a normal manner. When the at least one decoder cut-off relay receives a correct cipher, it would decode the cipher and make the circuit to enable starting of the car. No additional wiring is needed in installing the encoder/transmitter and the at least one decoder cut-off relay. The cipher type anti-theft system of the present invention can therefore be installed in a simpler and more convenient manner and would not be easily located by a theft by tracing any additional wiring in the car. Moreover, the encoder/transmitter of the anti-theft system of the present invention may be designed to be an independent and portable unit associated with a cigarette lighter, so that the cigarette lighter holder in the car may be used as an interface to receive the cipher without being easily located by the theft. Such cipher type anti-theft system may therefore effectively hamper the theft from driving the car away within a short time.